Reducing stress caused by thermal expansion of well pipe



Sept. 23, 1958 H. H. MEREDITH, JR

REDUCING STRESS CAUSED BY THERMAL ExPANsloN 0F WELL. PIPE Filed April 19. 1957 United States Patent O lREDUCING STRESS CAUSED BY THERMAL EXPANSIN F WELL PIPE Henry H. Meredith, Jr., Houston, Tex., assignor, by mesne assignments, to Jersey Production Research Company Application April 19, 1957, Serial No. 654,036

15 Claims. (Cl. 262-3) The present invention is directed to the mining of sulfur. More particularly, the invention is directed to reducing stress in pipe employed in the mining of sulfur, and the like. In its more specific aspects the invention is concerned with reducing and relieving stress caused by thermal expansion of pipe employed in the hot water mining of sulfur, and the like.

The present invention may be briefly described as a method for reducing stress in a water string of a well drilled to penetrate a sulfur-containing earth formation in which the water string is run into or lowered into the well to contact the bottom of the well with its lower end. In the present invention, the water string is suspended at the well head, and thereafter hot water is introduced through the water string into the sulfur-containing formation whereby the water string increases in length by thermal expansion. The weight of the water string is counterbalanced by imposing a sufficient force against the upper end of the water string whereby the lower end of the water string remains in contact with the bottom of the well and the upper end of the Water string moves upwardly and any force exerted on the bottom of the well by the water string is relieved.

It is contemplated in the present invention that, after suspending the water string at the well head, the weight of the water string may be counter-balanced prior to introducing hot water through the water string and thereafter the force against the upper end of the water string is maintained such that the lower end of the water string remains in contact with the bottom of the well while the upper end of the water string moves upwardly. The upper end of the water string may be raised in increments such that the weight of the pipe string may be transferred from the lower end of the pipe in increments to the upper end at the well head.

lt is contemplated further that the pressure imposed against the upper end of the water string may be hydraulic force, although other fluids may be used or other forces may be employed.

Since, in the present invention, the weight of the water string may be carried or supported by the surface casing on its upper end, it is contemplated that side forces resulting from the tendency of the surface casing to buckle may be transferred to a conductor pipe in which the surface` casing is arranged, whereby the stress on the water string is relieved and undue stresses on the surface casing are prevented. The side forces may suitably be transferred to the conductor pipe at a point or points intermediate to the ends of the conductor pipe.

In the completion of a sulfur well, the surface casing, which may be of 8%-inch outside diameter, is set in the `top of the cap rock, and after the hole has been drilled to the bottom of the sulfur zone, a water string, which may be of GSA-inch outside diameter, is set on the bottom of the well. Subsequently, the 3-inch sulfur string and the l-inch air line are run inside the water string. The water string is not supported at the surface, and all the weight of the water string is set on the bottom of the hole.

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Communication between the water string and the surface casing at the surface is prevented by a simple stuffing box pack off. In a well completed at 2500 feet, the weight of the water string in air causes a compressive stress at the bottom of the water string of 8500 pounds per square inch. While this stress may not be considered excessive, it causes the critical column length for 6%-inch, 20- pound per foot, 0.288-inch wall casing to be 35 feet, and the casing will buckle and touch opposite sides of the hole near the bottom for every 171/2 feet. While the fact that the column is continuous might allow it to be considered a fixed-ended column, the critical column length still may be as much as 70 feet, with the fact remaining that the column buckles, and failure may take place from bending stress were it not for lateral support received from the wall of the drilled hole.

ln production of a sulfur well the structural competence of the formation is reduced or destroyed by the removal of sulfur from the limestone formation. With the weight of the water string supported on the bottom of the well, the destruction of the structural competence of the formation allows the buckling of the casing to continue to a point where failure may result. It is believed that this phenomenon may be or is a contributory cause for failure of water strings in sulfur wells, and it is an object of the present invention to eliminate this source of stress to increase the productive life of sulfur wells. p

Water strings of casing are not suspended at Vthe surface in sulfur wells in the same manner as is common practice in oil wells because of the thermal expansion resulting from the introduction of hot water into the water string when the well is produced. Supporting the pipe on bottom and allowing the top of the Water string to move upwardly offers a simple way of eliminating the additional stressV that may be caused if the casing were restrained at both ends. The location of the perforations in the bottom joint of the water string for injection of water and for production of sulfur is considered critical, and the only manner in which the location of these perforations can be definitely established is by setting the casing on the bottom. The casing may be set to contact the bottom, but may be supported at the surface with no weight transmitted to the bottom ofthe hole. However, under these conditions, the thermal expansion in 2500 feet of pipe is 43 inches compared to the stretch of 31/2-inches to 4-inches originally introduced in the casing by its weight. Hence, the load is shifted back to the bottom of the string as soon as hot water is introduced. The water string could also be swung the required distance off the bottom so that when an increasing temperature is applied to the water string, it would be caused to elongate sufficiently to place the perforations at the proper location in the formation. This does not solve the problem, because the hole below the casing does not remain clear, and the pipe could not travel to the original bottom of the hole because of debris and formation material which settles into the bottom of the hole as a result of the operations v conducted therein. Therefore, stress would also be introduced into the water string. l

In accordance with the present invention, the problem of stress in water strings and in pipe employed in hot water sulfur mining operations is solved by suspending the water string at its upper end at the well head and counterbalancing the weight of the pipe with hydraulic force imposed against the upper end of the pipe such that on introduction of hot water into the water string, the thermal expansion of the water string causes the upper .end to move upwardly while the lower end of the pipe remains in contact with the bottom of the hole and with the perforations remaining at the desired locations.

The present invention will be further illustrated b reference to the vdrawing in which:

Fig. 1 is a showing of the several strings employed in a sulfur mining operation in accordance with the present invention; and

Fig. 2 is a detailed view partially in section of the upper end of the wall of Fig. 1 showing apparatus for carrying out the present invention.

Referring now to the drawing, in which identical numerals will be employed to designate identical parts, numeral 11 designates the earths surface from which a well 12 is drilled through a conductor pipe 13 driven to a desired distance and through which the well 12 is drilled. The well 12 is drilled to penetrate the cap rock 14, which may be a sulfur-bearing limestone formation although other minerals may be produced by hot water mining. A

surface casing 15 is cemented in the well 12 by cement 16, and thereafter a water string 17 is run in through the surface casing 15 to the bottom of the hole 12, with the water string 17 in contact with the bottom 18. The water string 17 is also provided with upper perforations 20 and lower perforations 21. Hot water ows through the upper perforations 20 into the formation 14, while molten sulfur enters the lower portion of the water string 17 through the perforations 21, a packer 22 being provided to cause the molten sulfur to enter a sulfur pipe 23 through which the sulfur is conveyed to the surface 11. An air pipe 24 is run in through the sulfur pipe 23 for introduction of air into the annulus 25 between the air pipe 24 and the interiorsurface of the sulfur string 23 to lift the molten sulfur to the surface by air lift. Connected to the water string 17 by a suitable flanged or screwed connection 26 is a flexible connection 27 for introducing hot water into the water string 17, a flexible connection 28 and a stuing box 28a for withdrawing sulfur from the sulfur pipe 23, and a flexible connection 29 and a stuffing box 29a for introducing air into the air pipe 24.

The outer surface of the surface casing 12 is provided with iluted circular support rings 30 which serve to transfer lateral forces resulting from the tendency of the surface casing to buckle to the conductor pipe 13 as will be explained hereinafter.

The upper end of the surface casing is provided with a conduit 31 provided with a valve connection 32, which communicates with an outlet 33 in the well head equipment generally designated by the numeral '34. Conduit 31 and outlet 33 comprise the usual well head connection and fill-up line for use during drilling operations for uid circulation or to control the well.

The well head equipment 34 has a flange connection 35 which is connected by suitable bolts 36. The well head connection generally designated by the numeral 34 is comprised of a lower section 38b and an upper section 38a. The lower section 38b has the port 33 connecting to the conduit 31 and is formed to provide a slip bowl 39, in which is arranged stationary slips 40. The upper section 38a is formed to provide a piston cylinder 41 in which is arranged a piston 42 shaped to form a second slip bowl 43 in which is arranged movable slips 44. The flange 35 is formed in two parts, with the upper part having a dependent annular section 45 resting on a shoulder 46 of the member 38b. The dependent annular member 45 is suitably sealed against the lower section 38b by means of a sealing member 47 and is suitably sealed against the water string 17 by sealing means 48.

The piston 42 is sealed against the inner surface of the member 38a by a sealing member 49 and against the water string 17 by sealing member 50. Sealing members 47, 48, 49, and 50 may suitably be O-rings provided in recesses in the members 42 and 45, but which may suitably be in either of the members 38a and 38b in contact with the members 42 and 45. Communication is had with the piston cylinder 41 through a port 51 communicating with a pressure conduit 52 controlled by valve 53 connected to a source of hydraulic fluid, not shown, and by means of a port 54 connected by a conduit 55 controlled by valve 56 and also connected to the source of hydraulic uid.

The upper end of the piston cylinder 41 is provided with an annular pack off member 57, which allows slidable restricted upward movement of the piston 42 and serves as a stop therefor and provides a means for forcing the piston back to its lower position.

In practicing the method of the present invention, a well would be drilled and arranged as shown in the drawing which may be an offshore sulfur well or which may be a conventional land well. In this particular instance, it is assumed that a l6inch conductor pipe 13 is driven from the surface 11 and an 85s-inch surface casing 15 is set and cemented with cement 16 in the top of the cap rock 14. The well head equipment, generally indicated by the numeral 34, is then placed and a 77/s-inch hole is then drilled to the bottom 18 and the 65/s-inch water string 17 is run in and set on bottom. The stationary 6%-inch slips 40 are inserted in the slip bowl 39, and the other equipment, including the movable slips 44, are installed and the casing or well head equipment bolted with the bolts 36. After running in the 31/2-inch sulfur string and the l-inch airline, hot water is then introduced through the water string 17. The thermal expansion normally encountered would obtain here, and the upper end of the water string 17 would extend through the well head equipment 34 approximately 43 inches, assuming the length of the water string to be 250G-feet. This is given by way of example only and not by way of limitation. The movable slips 44 would be utilized by applying the proper hydraulic pressure through the pressure connection conduit 55, causing upward movement of the piston 42, with upward movement of the slips 44 and the water string 17 at this point, until the entire weight of the water string 17 is transferred from the bottom 18 to the slips 44. If the stroke of the piston 42 is insufficient to lift all of the weight of the water string 17, pressure may be relieved at the lower pressure connection by manipulating valve 56 connecting to a suitable vent (not shown) allowing the load of the water string 17 to be transferred to the stationary slips 40. After the weight has been transferred to the stationary slips 40, the piston 42 and the movable slips 44 may be returned to their lower position by external manual force, or by applying the proper hydraulic pressure through the pressure conduit 52 and pressure connection 51. By manipulating valve 53 connected to a suitable vent (not shown) the pressure above piston 42 in cylinder 41 may be relieved and pressure may again be applied through the pressure port 54 connected through conduit 55 to cause the piston 42 and the slips 44 to move upwardly and carry the water string 17 therewith. As many lifts may be employed as required to transfer the total weight of the water string 17 from the bottom 18 of the well 12 to the slips 40 and 44. All compressive stresses in the lower end of the water string 17 are thus removed, eliminating any buckling of the water string 17 against the sides of the hole 12. Since the length of the Water string and also its weight are known, a sufficient amount of pressure is applied to the piston 42 to compensate for the weight of the water string. When this amount of pressure is applied to the piston 42, the weight of the water string is transferred from the bottom of the well to the slips 40 and 44 as has been described. The bottom end of the water string 17 does not move off bottom, and the water injection perforations and the sulfur production perforations 21 remain in the i position originally chosen for them.

Under some conditions, it is desirable to maintain the water string free of compressive forces, and under these conditions the water string 17 is run to the bottom 18 while supporting the water string 17 with suitable lifting equipment, such as elevators, not shown. The blowout preventers, not shown, may be lifted and stationary slips 40 placed in the well head 34. By slacking off on the hoisting equipment, the slips 40 would be set and the load transferred to them. Before injecting hot water into the well through the water string 17, pressure may be applied -unless some lateral or side support is given.

against piston 42 through port 54 and the pressure adjusted so that the load'of the water string 17 is transferred to the slips 44 without the water string 17 being lifted. Then, as hot water is introduced through the water string 17, thermal expansion and lengthening of the water string occurs, causing the water string to push against the bottom of the hole. By maintaining a uniform pressure under the piston 42 through port 54, the upper end of the water string 17 is caused to move upwardly without introducing any appreciable force or pressure of the pipe 17 against the bottom 18. As soon as a full stroke of the piston 42 has been made, pressure may be shifted to the upper pressure connection 51 connected to conduit 52 and the pipe load shifted to the stationary slips 40 with the piston 42 returning to its bottom position. Pressureis then imposed through the connection 54 and the piston 42 and slips 44 rise, lifting the water string 17 until it is again supported by -the movable slips 44. This operation is conducted until all thermal expansion of the water string 17 has occurred. y

During the life of the well subsidence of the cap rock 14 may occur, resulting in a lowering of the surface casing 15 relative to the water string 17. However, subsidence will not lower the water string, as its lower end is on the bottom 18 in Contact with the formation. As the relative motion of the surface casing 15 occurs with respect to the water string 17, there will be a tendency to shift the support of the water string 17 from the slips 40 or 44 to the bottom 18. However,'with the present invention, the piston 42 and slips 4l) may be moved to their lower position and the compressive stresses introduced into the water string 17 by any subsidence of the surface casing 15 may be relieved by lifting the water string 17 until it is again supported in the well head 34.

Support of the water string 17 in the well head equipment 34, as illustrated, causes compressive stresses to be introduced into the surface casing 15, since the well head 34 is attached thereto, as shown in the drawing. Supporting such a load in a Z500-foot well will cause the surface casing 15 to have a critical column length of approximately 55 feet, if it is assumed that its acts as a pinend connected column. The surface casing 15 will buckle It is contemplated that the side or lateral support may be obtained by attaching to the surface casing 15 iluted circular support rings 30 which just clear the inside diameter of the conductor pipe 13 packing the annulus with gravel or any other means whereby verticalv loads will not be transmitted to the conductor pipe. Placing the circular uted support rings 30 on less than SS-foot centers will prevent the surface casing 15 from buckling by adding the stiffness inherent in the conductor casing 13. The critical column length of the assembly is thereby increased to a column of 156 feet, which is sufficient to eliminate any danger of buckling as the 16-inch conductor pipe 13 will be braced to the producing platform on which the producing equipment is located at several points, and at no point does there exist a l56-foot unsupported interval.

While iluted circular supportrings have been shown for transferring the load laterally from the surface casing to the conductor pipe, other load transferring means, Such as slips, cement rings, metallic rings, and the like, may be employed located as has been described intermediate the ends of the surface casing the required distance for a specified length of pipe.

While the present invention has been described and illustrated with specific diameters of the several pipe strings and casing and for a specific depth of well, it is understood that these dimensions and lengths are given by way of illustration and not by way of limitation, since different dimensioned pipes may be employed for wells of dilerent depths.

It will be seen with the aforementioned description taken with the drawing and the mode of operation that an improved, useful and advantageous method has been li t) provided for eleminating stress caused by thermalex# pansion of pipe in sulfur mining and other operations where hot water is employed such as in dissolving subsurface beds of water soluble minerals.

The nature and objects of the present invention having been completely described and illustrated, what I wish t0 claim as new and useful and secure by Letters Patent is:

l. A method for reducing stress in a water string of a well drilled to penetrate a mineral containing earth formation in which the water string is run into the well to contact the bottom of the well with its lower end which comprises introducing hot water through the water string into the mineral-containing formation whereby the water string increases in length by thermal expansion, and counterbalancing the weight of the water string by imposing a suicient upward force against the upper end of said water string, whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly and any force exerted on the bottom of the well by Said water string is relieved.

2. A method in accordance with clairn'l in which the which the weight of the water string is counter-balanced by raising the upper end of the water string by increments.

3. A method in accordance with claim 1 in which the force is imposed against the upper end by hydraulic pressure.

4. A method for reducing stress in a Water string of a well drilled to penetrate a mineral containing earth formation in which the water string is run into the well and supported on the bottom of the well with its lower end, introducing hot water through the water string into the mineral-containing formation whereby the water string increases in length by thermal expansion, and counterbalancing the weight of the water string by imposing a sufcient upward force against the upper end of said water string, whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly and the force exertedvon the bottom of the well by said water string is relieved.

5. A method for reducing stress in a well drilled to penetrate a sulfur-containing-earth formation in which the water string is run into the well through surface casing arranged in a conductor pipe to contact the bottom of the well with its lower end which comprises introducing hot water through the water string into the sulfur-containing formation whereby the water string increases in length `by thermal expansion, counter-balancing the weight of the water string by imposing a sucient upward force against the upper end of said water string, whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly and any force exerted on the bottom of the well by said water string is relieved, supn porting the weight of the water string on the upper end of the surface casing, and supporting the surface casing laterally on the conductor pipe.

6. A method in accordance with claim 5 in which the surface casing is supported laterally on the conductor pipe at a plurality of points intermediate its ends.

7. A method for reducing stress in a water string of a well drilled to penetrate a mineral containing earth formation in which the water string is run into the well to contact the bottom of the well with its lower end which comprises counter-balancing the weight of the water string by imposing a suflicient force against the upper end of said Water string, introducing hot water through the water string into the mineral-containing formation whereby the water string increases in length by thermal expansion, and maintaining said force against the upper end of said water string whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly without the lower end of the water string exerting any force on the bottom yof the well. v

8. A method for reducing stress in a Water string of a well drilled to penetrate a sulfur-containing earth formation in which the water string is run into the well to contact the bottom of the well with its lower end which comprises counter-balancing the weight of the water string by imposing a suieient hydraulic force in increments against the upper end of said water string, introducing hot water through the water string into the sulfurcontaining formation whereby the water string increases in length by thermal expansion, and maintaining said force against the upper end of said water string whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly without the lower end of the water string exerting any force on the bottom of the well.

9. A method for reducing stress in al well drilled to penetrate a sulfur-containing earth formation in which the water string is run into the well through surface casing arranged in a conductor pipe to contact the bottom of the well with its lower end which comprises counterbalancing the weight of the water string by imposing a suicient force against the upper end of said water string, introducing hot water through the water string into the sulfur-containing formation whereby the water string increases in length by thermal expansion, maintaining said force against the upper end of said water string whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly without the lower end of the water string exerting any force on the bottom of the well, supporting the weight of the water string on the upper end of the surface casing, and transferring any side forces resulting from the tendency of the surface casing to buckle to the conductor pipe at a point intermediate its ends.

10. A method for reducing stress in a water string of a well drilled to penetrate a sulfur-containing earth formation which comprises lowering the water string in said well until its lower end contacts the bottom of the well, suspending said water string at the well head, introducing hot water through the water string into the sulfurcontaining formation whereby the water string increases in length by thermal expansion, and counter-balancing the weight of the water string by imposing a suthcient force against the upper end of said water string, whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly without the lower end of the water string exerting any force on the bottom ot' the well,

l1. A method for reducing stress in a water string of a well drilled to penetrate a sulfur-containing earth formation which comprises lowering the water string in said well until its lower end contacts and restson the bottom of the well, suspending said water string at the well head, introducing hot water through the water string into the sulfur-containing formation whereby the water string increases in length by thermal expansion, and counter-balancing the weight of the water string by imposing incrementally a suieient hydraulic force against the upper end of said water string, whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly and any force exerted on the bottom of the well by said water string is relieved,

12. A method for reducing stress in a water string of a well drilled to penetrate a sulfur-containing earth formation which comprises lowering the water string in said well until its lower end contacts the bottom of the well without exerting any substantial force on the bottom of the well, movably suspending said water string at the well head, counter-balancing the weight of the water string by imposing a suicient hydraulic force against the upper end of said water stringi11troducing hot water through the water string into the sulfur-containing formation whereby the water string increases in length by thermal expansion, and maintaining said force against the upper end of said water string whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly without the lower end of the water string exerting any force on the bottom of the well.

13. A method for reducing stress in a water string of a well drilled to penetrate a sulfur-containing earth formaich which comprises lowering the water string in said well until its lower end contacts the bottom of the well without exerting any substantial pressure on the bottom of the well, movably suspending said water string at the well head, counter-balancing the Weight of the water striptr by imposing a sufficient hydraulic force against the upper end of said water string, introducing hot water through the water string into the sulfur-containing formation whereby the water string increases in length by thermal expansion, and maintaining said hydraulic force against the upper end of said water string by imposing said force in increments as the length of said pipe increases whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly without the lower end of the water string exertingV any torce on the bottom of the well.

14. A method for reducing stress in a well drilled to penetrate a sulfur-containing earth formation which comprises lowering the water string in said well through surface casing arranged in a conductor pipe until its lower end contacts the bottom of the well without exerting any substantial force on the bottom of the well, movably suspending said water string at the well head, counter-balancing the weight of the water string by imposing a suicient force against the upper end of said water string, introducing hot water through the water string into the sulfur-containing formation whereby the water string increases in length by thermal expansion, maintaining said force against the upper end of said water string whereby the lower end of said water string remains in contact with, the bottom of the well and the upper end of said water string moves upwardly without the lower end of the water string exerting any force on the bottom of the well, supporting the weight of the water string on the upper end of the surface casing, and supporting the surface casing laterally on the conductor pipe at a point intermediate its ends.

15. A method for reducing stress in a water string of a well drilled to penetrate a sulfur-containing earth formation in which the Water string is run into the well to contact the bottom of the well with its lower end which comprises introducing hot Water through the water string into the sulfur-containing formation whereby the water string increases in length by thermal expansion, and counter-balancing the weight of the water string by imposing a suthcient upward force against the upper end of said water string, whereby the lower end of said water string remains in contact with the bottom of the well and the upper end of said water string moves upwardly and any force exerted on the bottom of the well by said water string is relieved.

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